Analysis And Study Of Reducing Energy Quality Loss In District Heating System

Faced with a grim situation of energy shortage and environmentaldegradation, exploring potential heat sources by applying waste energy andreducing the consumption of fossil fuel in district heating system of northerncities, is very important to realize the goal of energy conservation and emissionreduction. The base of rational use for multiple heat sources is theunderstanding of energy quality, and reducing the energy quality loss in districtheating system is the key to ensure waste heat utilization and energy efficiency.This paper applied entransy which describes the heat transfer ability to thedistrict heating system and analyzes the energy quality loss of differentsubsystem such as heat source and distribution systems during full timeoperation, and discusses the optimization methodology of reducing energyquality loss.First of all, the district heating system is considered as a multiple heattransfer process with constant heat flow and the model in which the entransyanalysis can be applied is established. By using the T-Q diagram, the basic typesof entransy dissipation in district heating system are discussed. Furthermore, theentransy dissipation of different parts in district heating system is analyzed indetail, which lays the foundation of optimization methodology of reducingentransy dissipation.For reducing the entransy dissipation during heat transfer in heat sources,by analyzing the features of energy quality loss in different types of districtheating systems, this paper points out the unmatched thermal capacity betweenthe heat source fluid and water in distribution system is the key factor causingenergy quality loss, and put forward the solution to improve the matchingbetween heat source and primary network by integration of multiple heatsources. On base of this idea, the optimization methodology of three differentheating systems is analyzed. For CHP system, the Co-ah system is analyzed. Forgas boiler system, a total heat recovery technology for flue gas is proposed. Forindustrial waste heat utilization, the tangent point analysis for heat extraction process design is put forward in order to optimize the heat integration ofindustrial waste heat.For reducing entransy dissipation during distribution, the impact ofparameters in primary network on reducing energy quality of heat sources isfocused on and it turns out that reducing the return water temperature of primarynetwork is better. In order to reach this goal, this paper analyzes differenttechnology to reduce entransy dissipation in distribution system. In substations,the heat transfer efficiency should be improved and the absorption heat pumpcan be very effective. In terminals, the floor heating and multiple terminals inseries can reduce the entransy dissipation markedly.For reducing the entransy dissipation during full time operation, this paperindicates that the traditional CHP systems have poor regulation performance inenergy quality and the entransy dissipation is worse at low load rate, but CHPwith waste heat recovery can realize the adjustment of heat source energyquality with a combination of both extracted and condensing steam. Theindustrial waste heat is not suitable for regulation and it should be integratedwith high quality heat source for regulation. Besides that, the constant flowcontrol for the primary network is more suitable for reducing energy quality lossduring full time operation.In the end, the results of analysis are applied for the urban energy planningof Chifeng city. By analyzing the current and all the potential heat sources, theannual urban energy planning is designed aiming at applying waste heat andimproving energy efficiency.